Process for the manufacture of 2,3,3,3-tetrafluoropropene by gas phase fluorination of pentachloropropane

ABSTRACT

The present invention provides a process of catalytic fluorination in gas phase of product 1,1,1,2,3-pentachloropropane or/and 1,1,2,2,3-pentachloropropane into product 2,3,3,3-tetrafluoropropene in presence of a catalyst.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. patent application Ser. No.15/008,896, filed Jan. 28, 2016, now allowed; which is a Continuation ofU.S. patent application Ser. No. 13/980,669, filed Sep. 26, 2013, issuedas U.S. Pat. No. 9,278,895; which is a National Stage application ofInternational Application No. PCT/IB2011/000313 filed Jan. 21, 2011,each of which is incorporated by reference herein.

FIELD OF THE INVENTION

The aim of the invention is the catalytic fluorination in gas phase ofproduct 1,1,1,2,3-pentachloropropane (HCC 240db) and/or1,1,2,2,3-pentachloropropane (HCC 240aa) into product2,3,3,3-tetrafluoropropene (HCFO 1234yf).

TECHNICAL BACKGROUND

The protocol of Montreal for the protection of the ozone layer led tothe end of the use of chlorofluorocarbons (CFCs). Less aggressivecompounds for the ozone layer, such as the hydrofluorocarbons (HFCs)e.g. HFC-134a replaced chlorofluorocarbons. These latter compounds wereindeed shown to provide greenhouse gases. There exists a need for thedevelopment of technologies, which present a low ODE (ozone depletionpotential) and a low GWP (global warming potential). Although thehvdrofluorocarbons (HFCs), which are compounds which do not affect theozone layer, were identified as interesting candidates, they exhibit arelatively high GWP value. There still exists the need to find compoundswhich exhibit a low GWP value. Hydrofluoroolefins (HFO) were identifiedas being possible alternatives with very low ODE and OWE values.

Several processes for production of HFOs compounds, in particular ofpropenes, were developed. The two compounds 1233xf(2-chloro-3,3,3-trifluoropropene) and 1234yf(2,3,3,3-tetrafluoropropene) are particularly desired.

US2009/0240090 discloses the gas-phase reaction of1,1,1,2,3-pentachloropropane (HCC 240db) into product2-chloro-3,3,3-trifluoropropene (HCFO 1233xf) (in the absence ofoxygen). The catalyst used in Example 3 is fluorinated Cr₂O₃. Theproduct 1233xf thus produced is then converted into product2-chloro-1,1,1,2-tetrafluoropropane (244bb) in a liquid phase reaction.

WO2009/015317 discloses the reaction of a chlorinated compound, whichcan be 1,1,2,3-tetrachloro-1-propene (1230xa),1,1,1,2,3-pentachloropropane (240db) or 2,3,3,3-tetrachloro-1-propene(1230xf) with HF, in gas phase, on a catalyst and in the presence of atleast one stabilizer. This process allows obtaining2-Chloro-3,3,3-trifluoro-1-propene (1233xf). No working example isprovided with 240db as a starting material. The stabilizer is said toimprove catalyst lifetime. It is also mentioned that periodicregeneration is considered.

WO2005/108334, example 3, discloses that 240db is passed through a flowreactor for a contact time for about 5 to 50 seconds at about 250-400°C. in the presence of 5 molar excess of HF over a 50 g ⅛-inch Cr₂O₃catalyst bed to give 244db (2-chloro-1,1,1,3-tetrafluoropropane). It isfurther indicated that the 244db is then dehydrochlorinated by passingit over a Cr₂O₃ catalyst (50 g) at 425-550° C. with a contact time of 25to 30 seconds to afford product 1234ze (1,3,3,3-tetrafluoropropene).

GB-A-1091103 discloses a process for manufacturing a chromiumfluorination catalyst. Numerous compounds that may be fluorinated usingthis catalyst are indicated: pentachloropropane is mentioned amongothers, while not being the preferred compound.

WO2010/123148 discloses the fluorination of 240db into 1293xf, in theabsence of catalyst.

Thus, there is still a need for processes for the production of compound1234yf.

SUMMARY OF THE INVENTION

The invention provides single stage process of catalytic fluorination ingas phase of product 1,1,1,2,3-pentachloropropane or/and1,1,2,2,3-pentachloropropane into product 2,3,3,3-tetrafluoropropene inpresence of a catalyst, where the process is preferably continuous. Theprocess is a single stage process, preferably carried out in onereactor, more preferably in one catalytic bed.

Embodiments are the following:

-   The product 2,3,3,3-tetrafluoropropene is present at a concentration    of at least 1%, preferably more than 2%, more preferably more than    3%.-   The catalyst is a chromium catalyst, supported or unsupported,    preferably unsupported.-   The catalyst further comprises a co-catalyst selected from Ni, Co,    Zn, Mn, Mg or mixtures thereof, preferably nickel or magnesium, and    wherein said co-catalyst is preferably present in an amount from    about 1-10 wt % of said fluorination catalyst.-   The process is carried out in the presence of a catalyst comprising    Ni—Cr, preferably supported.-   The catalyst is supported on a support selected from fluorinated    alumina, fluorinated chromia, fluorinated activated carbon or    graphite carbon.-   The fluorination catalyst is activated with a fluorine-containing    compound, preferably hydrogen fluoride.-   The 1,1,1,2,3-pentachloropropane contains up to 40 mol % of isomer    1,1,2,2,3-pentachloropropane.-   The process is carried out, at a pressure from 3 to 20 bars,    preferably 5 to 15 bars, more preferably 7 to 10 bars.-   The process is carried out at a temperature of from 200 to 450° C.,    preferably from 300 to 430° C., more preferably from 320 to 420° C.-   The process is carried out with a contact time from 6 to 100 sec,    preferably from 10 to 80 sec, more preferably from 15 to 50 sec.-   The process is carried out with a molar ratio H:240 from 3:1 to    150:1, preferably 4:1 to 70:1, more preferably 5:1 to 50:1.-   The process is carried out in the presence of a polymerization    inhibitor, preferably chosen from the group consisting of    p-methoxyphenol, t-amylphenol, limonene, d,1-limonene, quinones,    hydroquinones, epoxides, amines and mixtures thereof.-   The process is carried out in the presence of oxygen and/or    chlorine, preferably in an amount of from 0.05 to 15 mole %, more    preferably 0.3 to 10 mole % of oxygen or chlorine per    pentachloropropane molecule.-   The process comprises the steps of:    -   (i) contacting 1,1,1,2,3-pentachloropropane (HCC 240db) and/or        1,1,2,2,3-pentachloropropane (HCC 240aa) with hydrogen fluoride        HF in gas phase in the presence of a fluorination catalyst under        conditions sufficient to produce a reaction mixture comprising        2,3,3,3-tetrafluoropropene (1234yf);    -   (ii) separating the reaction mixture into a first stream        comprising 2,3,3,3-tetrafluoropropene (1234yf) and a second        stream comprising 2-chloro-3,3,3-trifluoro-1-propene (1233xf)        and 1,1,1,2,2-pentafluoropropane (245cb);    -   (iii) recycling at least a part of the second stream at least in        part back to step (i).-   The process comprises the steps of:    -   (i) contacting 1,1,1,2,3-pentachloropropane (HCC 240db) and/or        1,1,2,2,3-pentachloropropane (HCC 240aa) with hydrogen fluoride        HF in gas phase in the presence of a fluorination catalyst under        conditions sufficient to produce a reaction mixture comprising        2,3,3,3-tetrafluoropropene (1234yf);    -   (ii) separating the reaction mixture into a first stream        comprising HCl, 2,3,3,3-tetrafluoropropene (1234yf) and a second        stream comprising HF, 2-chloro-3,3,3-trifluoro-1-propene        (1233xf) and 1,1,1,2,2-pentafluoropropane (245cb);    -   (ii) recycling at least a part of the second stream at least in        part back to step (i).-   The first stream may be further separated into HCl and    2,3,3,3-tetrafluoropropene (1234yf), preferably in a distillation    step.-   The process comprises the steps of    -   (i) contacting 1,1,1,2,3-pentachloropropane (HCC 240db) and/or        1,1,2,2,3-pentachloropropane (HCC 240aa) with hydrogen fluoride        HF in gas phase in the presence of a fluorination catalyst under        conditions sufficient to produce a reaction mixture comprising        2,3,3,3-tetrafluoropropene (1234yf);    -   (ii) separating the reaction mixture into HCl and a stream        containing the fluorinated products;    -   (iii) separating said stream containing the fluorinated products        into a first stream comprising 2,3,3,3-tetrafluoropropene        (1234yf) and a second stream comprising HF,        2-chloro-3,3,3-trifluoro-1-propene (1233xf) and        1,1,1,2,2-pentafluoropropane (245cb);    -   (iv) recycling at least a part of the second stream at least in        part back to step (i).-   The separating step is a distillation step.-   The process is continuous.

BRIEF DISCLOSURE OF THE DRAWINGS

FIG. 1 is a scheme representing the process carried out in theinvention.

FIG. 2 is a scheme representing the process carried out in theinvention.

DETAILED DESCRIPTION OF EMBODIMENTS

The invention is based on the findings that 240db (and/or 240aa) can becatalytically fluorinated in gas phase in a single stage into 1234yf,and that process conditions can be selected so as to achieve a reactiondown to the final product. The stream obtained typically contains atleast 1% of 1234yf, preferably at least 2%, more preferably at least 3%(mol).

240db is reacted with HF in a Single reactor. The desired product is1234yf, while 1233xf is also seen upon conversion. The 1233xf thusformed in turns undergoes a series of possible reactions. Reaction withHF can lead directly to 1234yf. This unsaturated compound uponfluorination with HF, give 245cb. 1234yf and 245cb form an equilibrium;the invention is based on this finding. Any 245cb formed can be recycledto the first reaction zone, whereby the equilibrium is displaced (1234yfbeing thus prevented from further conversion into 245cb). The 245cb flowrate in the recycling loop (either at the exit of the gas-phase reactoror in the second stream back exiting the distillation column and back tothe gas-phase reactor) is thus substantially constant. No 245cb build upwill thus take place in the recycling loop. In this instance, 240db fedinto the reactor converts only into 1234yf (and possibly into 1233xf)since 245cb is already present in the recycling loop.

The catalyst used in the invention is for example a catalyst based on ametal including a transition metal oxide or a derivative or halide oroxyhalide such a metal. Catalysts are e.g. FeCl₃, chromium oxyfluoride,chromium oxides (that can optionally be subject to fluorinationtreatments), chromium fluorides, and mixtures thereof. Other possiblecatalysts are the catalysts supported on carbon catalysts based onantimony, catalysts based on aluminum (as AlF₃ and Al₂O₃ and oxyfluorideof alumina and aluminum fluoride). Generally speaking, catalysts thatcan be used are chromium oxyfluoride, aluminium fluoride andoxyfluoride, and supported or unsupported catalyst containing a metalsuch as Cr, Ni, Zn, Ti, Zr, Mo, Ge, Sn, Pb, Mg. Reference can also bemade to the disclosures of WO-A-2007/079431, at page 7, lines 1-5 and28-32, EP-A-939071, at paragraph [0022], WO2008/054781 at page 9 line topage 10 line 34, WO2008/040969 in claim 1, all incorporated herein byreference.

Prior to its use, the catalyst is subjected to activation, typicallywith HF, under suitable conditions.

A preferred embodiment uses a particular catalyst, which is a mixedcatalyst, containing both chromium and nickel. The molar ratio Cr:Ni,with respect to the metallic element is generally between 0.5 and 5, forexample between 0.7 and 2, including close to 1. The catalyst maycontain in weight from 0.5 to 20% chromium and 0.5 to 20% nickel,preferably between 2 and 10% of each metal.

The metal may be present in metallic form or as derivatives, includingoxide, halide or oxyhalide. These derivatives, including halide andhalide oxides, are obtained by activation of the catalytic metal.Although the activation of the metal is not necessary, it is preferred.

The support is preferably made from aluminum. There are several possiblecarriers such as alumina, activated alumina or aluminum derivatives.These derivatives include aluminum halides and halide oxides ofaluminum, for example described in U.S. Pat. No. 4,902,838, or obtainedby the activation process described below.

The catalyst may include chromium and nickel in a non-activated oractivated form, on a support that has been subjected to activation ornot.

Reference can be made to WO2009/118628, and especially to the disclosureof the catalyst from page 4, line 30 to page 7, line 16, which isincorporated herein by reference.

The catalyst can also be a high surface area Cr based catalyst which ispreferably unsupported. The catalyst can optionally contain a low levelof one or more co-catalyst such as Co, Zn, Mn, Mg and Ni salt. Apreferred co-catalyst is nickel or magnesium. Another preferredco-catalyst is Zn. Another preferred co-catalyst is Mg. A disclosure ofthe high surface area Cr based catalyst can be found in WO2009/158321,pages 4 and 6).

The process of the present invention is preferably run continuously,which from an industrial point of view is highly desirable.

The present fluorination process involves contacting 240db with HF inthe reaction zone in a gas phase, under conditions sufficient to convertthe 240db to fluorination products comprising mainly 1234yf.

Typically, the process of the invention is carried out with a molarratio HF:240 from 3:1 to 150:1, preferably 4:1 to 70:1, more preferably5:1 to 50:1.

Typically, the process of the invention is carried out at a pressurefrom 3 to 20 bars, preferably 5 to 15 bars, more preferably 7 to 10bars.

Typically, the process of the invention is carried out at a temperatureof from 200 to 450° C., preferably from 300 to 430° C., more preferablyfrom 320 to 420° C. The temperature of the bed can be substantiallyuniform in the reactor or can be adjusted along the path of the stream,decreasing or increasing along the direction of flow.

Contact times (catalyst volume divided by the total flow rate ofreactants and co-feeds, adjusted to the operating pressure andtemperature) are typically from 6 to 100 sec, preferably from 10 to 80sec, more preferably from 15 to 50 sec.

Conditions will be selected so as to promote the formation of the fullyfluorinated product. When low HF:organics ratios are used, longercontact times and higher pressure will generally be used, and especiallyhigher temperatures. High temperatures, typically above 360° C. withhigh pressure typically above 5 bars are generally preferred. Mildfluorination conditions may provide the 1233xf product, as is disclosedin the applicant's own patent application PCT/FR2010/052277

An oxygen or chlorine co-feed may be used to extend the catalystlifetime, typically in an amount of from 0.05 to 15 mole %, preferably0.5 to 10 mole % of oxygen or chlorine per pentachloropropane molecule.The oxygen can be introduced as an oxygen-containing gas such as air,pure oxygen, or an oxygen/nitrogen mixture.

A polymerization inhibitor can be used to extend the catalyst life,typically in a concentration of from about 50-1000 ppm, more preferablybetween 100-500 ppm. The polymerization inhibitor can bep-methoxyphenol, t-amylphenol, limonene, d,1-limonene, quinones,hydroquinones, epoxides, amines and mixtures thereof. The preferredpolymerization inhibitor is p-methoxyphenol or t-amylphenol. Theco-feeding of a low level of a polymerization inhibitor can control suchpolymerization of chloroolefins and extend the life of the catalyst asdescribed in U.S. Pat. No. 5,714,651, incorporated herein by reference.

1233xf may be produced along with 1234yf, and separation and recyclingof 1233xf and 245cb into the gas phase reactor is one embodiment of theinvention.

Hence, the invention also provides for a process comprising the stepsof:

-   -   (i) contacting 1,1,1,2,3 pentachloropropane (HCC 240db) and/or        1,1,2,2,3-pentachloropropane (HCC 240aa) with hydrogen fluoride        HF in gas phase in the presence of a fluorination catalyst under        conditions sufficient to produce a reaction mixture comprising        2,3,3,3-tetrafluoropropene (1234yf);    -   (ii) separating the reaction mixture into a first stream        comprising 2,3,3,3-tetrafluoropropene (1234yf) and a second        stream comprising 2-chloro-3,3,3-trifluoro-1-propene (1233xf);    -   (iii) recycling at least a part of the second stream at least in        part back to step (i).

This recycling can take various forms, as is depicted in the followingfigures.

FIG. 1 represents an embodiment of the process carried out in theinvention. The gas-phase reactor is fed with 240db and HF. The reactionmixture exiting the reactor mainly comprises HCl, 1233xf, unreacted HF,1234yf and 245cb. This reaction stream is separated by distillation intoa first stream (light products) comprising HCl, 1234yf (possibly with asmall amount of HF thereby forming an azeotropic mixture) and minoramounts of 245cb and 1233xf. A second, heavier, stream is obtained atthe bottom of the distillation column, and comprises mainly HF, 1233xfand 245cb. The lighter fraction containing HCl, 1234yf (with HF) andminor amounts other products is again distillated. The top flowcomprises HCl, while the bottom flow comprises 1234yf and HF, which canagain be separated using appropriate known methods. Among known methodsis the decantation, which produces an HF rich flow which can be recycledto the gas-phase reactor. This decreases the fluorine content downstreamin the process, generating less side-product (e.g. CaF₂ which must bediscarded). The streams exiting the decantation are treated according toknown methods, including washing and scrubbing and distillations.

FIG. 2 represents another embodiment, where HCl is removed in a firststep before distillation of the organic fluorinated products takesplace. The gas-phase reactor is fed with 240db and HF. The reactionmixture exiting the reactor comprises mainly HCl, 1233xf, unreacted HF,1234yf and 245cb. This reaction stream is separated by a firstdistillation into a stream containing mainly HCl and another streamcontaining the other products. This other stream is separated bydistillation into a first stream (light products) comprising 1234yf(possibly with a small amount of HF thereby forming an azeotropicmixture) and minor amounts of 245cb and 1233xf. A second, heavier,stream is obtained at the bottom of the distillation column, andcomprises mainly HF, 1233xf and 245cb. The lighter fraction containing1234yf (with HF) and minor amounts other products is obtained at the topof the second distillation tower. This top flow can again be separatedusing appropriate known methods. Among known methods is the decantation,which produces a flow of HF which can be recycled to the gas-phasereactor. This decreases the fluorine content downstream in the process,generating less side-product (e.g. CaF₂ which must be discarded). Thestreams exiting the decantation are treated according to known methods,including washing and scrubbing and distillations.

The reactants can be fed to the reactor at the same location, atdifferent locations, or using staged feeding at staged locations alongthe reactor. A preferred feeding system is to blow the gaseous reactantsat the bottom of the reactor. Recycling can be done at the entry of thereactor or at an intermediate stage of the reactor; preferably at theentry of the reactor. It is also possible to recycle part of the streamexiting the reactor.

Reactions are implemented in a dedicated reactor for reactions involvinghalogens. Such reactors are known to those skilled in the art and caninclude linings based e.g. Hastelloy®, Inconel®, Monel® orfluoropolymers. The reactor may also include means of heat exchange, ifnecessary.

The final product is readily recovered by any means known in the art,such as by scrubbing, washing, extraction, decantation and preferablydistillation. It can also be further purified by distillationtechniques.

EXAMPLES

The following examples illustrate the invention without limiting it.

The equipment used consists of a tubular reactor of an internal diameterof 28 mm, made of INCONEL® alloy 600 surrounded by a tubular oven. Thehomogeneity of temperature is ensured by fluidized corindon filling thespace between the reactor and the oven. It is also equipped withpressure and temperature controller. The reactants, preliminarilyvaporized thanks a heater, are introduced in gaseous phase at the bottomof the reactor. After the reactor, a regulation pressure valve allowsworking in a range of pressure between atmospheric and 16 bars absolute.

At the outlet of the set-up, the products of the reaction are washedthrough a water scrubber to remove hydracids. A sample is taken to beanalyzed off-line by a gas phase chromatography. Two different GCanalysis are necessary to detect the wide range of possible products:the boiling point can vary from −28.3° C. for the 1234yf to 192° C. forthe raw material, 240db.

The analysis by chromatography is carried out using a column CP Sil 8CB,dimensions 50 m*0.32 mm*5 μm, for the detection of heavier products like240db. The programming of temperature of the oven is the following one:70° C. during 10 min then slope of 10° C./min until 2.50° C.

The analysis by chromatography is carried out using a column Carbopack B1% SP1000-60/80 mesh-5 m for quantification and better separation oflighter products. The programming of temperature of the oven is thefollowing one: 40° C. during 10 min then slope of 4° C./min until 180°C.

The resulting composition is given in molar %.

The molar ratio of HF (MR HF) is defined as the ratio between the molarflow rate of HF and the molar flow rate of 1,1,1,2,3-pentachloropropane.

Example 1 (Not According to the Invention)

Fluorination of 240db (1,1,1,2,3-pentachloropropane) is performed in thereactor described above with 79.4 cm³ of Ni—Cr catalyst supported onAlF₃.

The catalyst used is a mixed catalyst nickel/chromium of atomic ratio ofNi/Cr=1, supported on alumina fluoride and is prepared by impregnatingsolutions of nickel and chromic anhydride (CrO₃). After impregnation anddrying, the Solid is treated at a temperature between 320° C. and 390°C. in the presence of a mixture of hydrofluoric acid and nitrogen(concentration by volume of 5 to 10% of this acid in nitrogen.).

The reactor was continuously fed with 15 g/hr of anhydrous HF and about4.5 g/hr of 1,1,1,2,3-pentachloropropane at atmospheric pressure for 86hrs. Thus, the contact time is 7.4 seconds, the molar ratio of HF to 240is 36, and the reaction temperature is 340° C. The amount of oxygen isabout 4 mol % with respect to the 240db. Results are given in the table1.

Example 2 (Not According to the Invention)

Fluorination of the mixture of 65.9 mol % of 240db or1,1,1,2,3-pentachloropropane and 34.9 mol % of 240aa or1,1,2,2,3-pentachloropropane is performed according to example 1described above. The reactor was continuously fed with 16 g/hr ofanhydrous HF and about 5.1 g/hr of 1,1,1,2,3-pentachloropropane atatmospheric pressure. Thus, the contact time is 6.9 seconds, the molarratio is 34, and the reaction temperature is from 340° C. The amount ofoxygen is about 4 mol % with respect to the total number of mole of1,1,1,2,3-pentachloropropane and 1,1,2,2,3-pentachloropropane. Resultsare given in table 1.

Examples 3 and 4 (Not According to the Invention)

Example 2 is repeated at different temperatures as indicated in table 1.

TABLE 1 Outlet gas molar composition (%) Temp. pentachloro- 1234yf + °C. propane 245cb 1233xf Others Ex. 1 340 0 1.6 98.3 0 Ex. 2 340 0 0.572.0 25.6 Ex. 3 360 0 0.5 72.0 25.1 Ex. 4 380 0 0.6 74.3 22.8

Use of a low pressure together with rather low temperature does notallow 1234yf to be produced in significant amount.

Example 5 (According to the Invention)

Fluorination of 240db (1,1,1,2,3-pentachloropropane) is performed in thereactor described above with 150 cm of Ni—Cr catalyst supported on AlF₃.

The catalyst used is a mixed catalyst, nickel/chromium of atomic ratioof Ni/Cr=1, supported on alumina fluoride and is prepared byimpregnating solutions of nickel and chromic anhydride (CrO₃). Afterimpregnation and drying, the solid is treated at a temperature between320° C. and 390° C. in the presence of a mixture of hydrofluoric acidand nitrogen (concentration by volume of 5 to 10% of this acid innitrogen).

The reactor was continuously fed with 33 g/hr of anhydrous HF and about3.9 g/hr of 1,1,1,2,3-pentachloropropane at 3 bars absolute for 550 hrs.Thus, the contact time is 20 seconds, the molar ratio of HF to 240 is40, and the reaction temperature is 300° C. The amount of oxygen isabout 4 mol % with respect to the 240db. Results are given in the table2.

TABLE 2 outlet gas composition with time. Catalyst Outlet gas molarcomposition (%) age (h) CO₂ 245cb 1234yf 1233xf 243db X* 23 0.41 2.2 2.292.6 0.05 2.54 49 0.39 1.4 1.9 93.7 0.54 2.07 71 0.37 0.92 1.7 94.2 0.672.14 96 0.29 0.69 1.4 94.8 0.74 2.08 Products X include 143a, 1234ze,245fa, 152a, 1233zd, 243ab, 1232xf, 1223xd. 240db was never detected.

Example 6

Example 5 is repeated at different temperatures as indicated in table 3.Points are recorded after around 200 h run.

TABLE 3 Impact of temperature of the reaction on the gas composition. TOutlet gas molar composition (%) (° C.) 245cb 1234yf 1233xf 243db X 3260.40 1.46 95.3 0.33 1.69 350 0.88 2.29 94.3 0.14 1.15 374 0.79 2.81 93.40.13 1.68 Products X include 143a, 1234ze, 245fa, 152a, 1233zd, 243ab,1232xf, 1223xd. 240db was never detected.

The increase of the temperature helps the fluorination towards 1234yfand 245cb.

Example 7

This example provides the effect of recycling.

Fluorination is performed in the reactor described above with 100 cm³ ofNi—Cr catalyst supported on AlF₃. The pressure is 8 bars absolute andthe temperature is 350° C. The contact time is 20 s, the molar ratio ofHF to the sum of the organics is around 40 and the molar ratio of oxygento the sum of the organics is 4%. The molar composition between theinlet and the outlet is given in table 4. The products that are recycledcontain 1233xf and 245cb. Table 4 contains the expected data obtained byrecycling.

TABLE 4 Mol % 240db 1233xf 1234yf 245cb 243db others Inlet 50 47.5 0.30.1 0.7 1.4 Outlet 0 86.0 3.8 5.2 1.3 3.7

The invention claimed is:
 1. A process for producing2,3,3,3-tetrafluoropropene (1234yf) comprising: introducing1,1,1,2,3-pentachloropropane (240db) and/or 1,1,2,2,3-pentachloropropane(240aa), HF, and a first mixture comprising 1,1,1,2,2-pentafluoropropane(245cb), 2-chloro-3,3,3-trifluoropropene (1233xf) and2,3,3,3-tetrafluoropropene (1234yf) into a gas phase fluorinationreactor containing a fluorination catalyst, wherein at least a part ofthe 245cb introduced to the reactor is provided from a recycle loop, and(ii) producing 1234yf and 1233xf in the reactor, wherein 1234yf andrecycled 245cb form an equilibrium in the reactor thus resulting inincreased production of 1234yf and a constant rate of 245cb in therecycle loop.
 2. The process of claim 1, wherein the1,1,1,2,3-pentachloropropane (240db) and/or 1,1,2,2,3-pentachloropropane(240aa), HF, and first mixture are introduced to the reactor underconditions sufficient to produce a reaction mixture comprising2,3,3,3-tetrafluoropropene (1234yf), 2-chloro-3,3,3-trifluoro-1-propene(1233xf) and 1,1,1,2,2-pentafluoropropane (245cb), the process furthercomprising; (iii) separating the reaction mixture into a first streamcomprising 2,3,3,3 tetrafluoropropene (1234yf) and a second streamcomprising 2-chloro-3,3,3-trifluoro-1-propene (1233xf) and1,1,1,2,2-pentafluoropropane (245cb); and (iv) recycling at least a partof the second stream back to step (i).
 3. The process of claim 1,wherein the process is carried out in a single stage.
 4. The process ofclaim 1, wherein the product 2,3,3,3-tetrafluoropropene is present at aconcentration of at least 1%.
 5. The process of claim 1, wherein saidcatalyst is a chromium catalyst.
 6. The process of claim 4, wherein saidcatalyst further comprises a co-catalyst selected from the groupconsisting of Ni, Co, Zn, Mn, Mg and mixtures thereof, and wherein saidco-catalyst is present in an amount from about 1-10 wt % of saidfluorination catalyst.
 7. The process of claim 1, wherein the process iscarried out in the presence of a catalyst comprising Ni—Cr.
 8. Theprocess of claim 1, wherein said catalyst is supported on a supportcomprising fluorinated alumina, fluorinated chromia, fluorinatedactivated carbon or graphite carbon.
 9. The process of claim 1, whereinthe fluorination catalyst is activated with a fluorine-containingcompound.
 10. The process of claim 1, wherein the1,1,1,2,3-pentachloropropane contains up to 40 mol % of isomer1,1,2,2,3-pentachloropropane.
 11. The process of claim 1, wherein theprocess is carried out at a pressure from 3 to 20 bars.
 12. The processof claim 1, wherein the process carried out at a temperature of from 200to 450° C.
 13. The process of claim 11, wherein the process carried outat a temperature of 350 to 450° C.